Thoriated tungsten filament or wire and method of making same



Oct. 11, 1966 H. J. EHRINGER 3,278,281

THORIATED TUNGSTEN FILAMENT OR WIRE AND METHOD OF MAKING SAME FiledSept.r 15, 1957 4 Sheets-Sheet 1 (Ff/P @5A/r ar Fys/av Car/wwf) INVENTR.,L/f/PMm//Y J. EMP/N65?.

BY WQ/mm,

THC@ 0F MAKING SAME ct. l1, 1966 W IRE AND THORIATED TUNGSTEN FILAMENTOR Filed Sept. 13, 1957 4 Sheeus-Sheec 2 fvwm/5% @et i966 HL J. THORATEDTUNGSTEN FLAMEI'T OR WIRE AND METHOD OF MAKING SAME Filed Sept. l5, 1957e Sheds-Sheet 5 INVENTOR. /L/E/V/W//V J." THE/N657? @ct H, 966 H. J.EHRINGER 3,278,281

THORIATED TUNGSTEN FILAMENT OR WIRE AND METHOD OF MAKING SAME FiledSept. 13, 1957 4 Sheets-Sheet 4 @m0/aim United States Patent O 3,278,281THORIATED TUNGSTEN FILAMENT R WIRE AND METHOD 0F MAKING SAME Hermann J.Ehrnger, West Orange, NJ., assignor to Westinghouse ElectricCorporation, East Pittsburgh,

Pa., a corporation of Pennsylvania Filed Sept. 13, 1957, Ser. No.683,809 19 Claims. (Cl. 29-182.5)

This application is a continuation-in-part of my copending applicationSerial No. 683,361, filed September l1, 1957, now abandoned, and ownedby the assignee of the presentY application.

This invention relates to filament wire and filaments for incandescentlamps and to methods for making such wire and, more particularly, to ashock-resistant, vibration-resistant and non-sag filament wire andfilaments `suitable for use in incandescent lamps and to a method formaking such filament wire.

The impact resistance of the usual incandescent lamp filaments is verypoor when the unenergized filaments are subjected to shock andvibration. Even when energized, the impact resistance of such filamentsunder conditions of shock and vibration is quite poor. In the earlydevelopment of tungsten filaments for incandescent lamps, the filamentsbroke easily and sagged greatly after initial energization, whichresulted in very poor performance for the incandescent lamps.Thereafter, socalled doping impurities were added to the tungstenfilaments, which doping impurities improved the filament strength anddirected the tungsten grain growth within the energized filaments, inorder to form what are known as interlocking crystals or grains. Thesedoping impurities drastically improved the performance of incandescentlamps and revolutionized the industry. One of the first doping additiveswhich was utilized was thorium oxide and this doping additive served tostrengthen the filament against shock and vibration, although thethoria-doped wire had very poor non-sag characteristics.

The use of thoria as a doping additive to a tungsten filament wassuperseded by later-developed doping additives, since these gave muchbetter non-sag characteristics. In the present practices potassium,alumina, and silica are added as potassium chloride, potassium silicateand aluminum chloride, for example, and are used as doping additives.These materials are normally added to the tungstic oxide or to acid,before the tungsten is sintered as an ingot and thereafter swaged anddrawn into wire. As an example, residual doping constituents afterreduction may comprise 0.3% by weight potassium, 0.02% by weightalumina, and 0.4% by weight silica. These doping constituents may varyboth in amount and formulation, but the foregoing are representative ofthe present practices.

The foregoing potassium, alumina, and silica-doped wire possessesexcellent non-sag characteristics, but the impact resistance of suchWire when subjected to vibration or shock is comparatively poor. Becauseof its excellent non-sag characteristics, however, it is normally usedin applications where non-sag, vibration-resistant and .shockresistantcharacteristics are required. This has resulted in extremely poor lifein such applications as dashboard and trunk lights for automobiles andtoy electric trains, for example, where the lamps are subjected toconsiderable shock and vibration.

When an incandescent lamp filament coil sags the longitudinal coildimension increases. This alters the lumen output of the lamp andusually causes turns of the filament coil to short out, with resultantfailure. The term non-sag is normally used in the .art to describe afilament coil which has sufficient resistance to coil elongation tocause the lumen output of the lamp to be rel- ICC atively uniform and toprevent turns of the filament coil from shorting out to cause prematurefai-lure. This is the meaning given to the term non-sag as used herein.

In order -to avoid and overcome the foregoing and other difficulties ofand objections to the practices of the prior art, it is the generalobject of this invention to provide a shock resistant,vibration-resistant and non-sag filament wire suitable for use inincandescent lamps.

It is a further object to provide a shock-resistant, vibration-resistantand non-sag filament suitable for use in incandescent lamps.

It is another object to provide a shock-resistant, vibration-resistantand non-sag filament suitable for use in incandescent lamps, wherein thefilament comprises a plurality of interlocking crystals or grains whichare maintained as such.

It is a still further object to provide a process for formingshock-resistant, vibration-resistant, and non-sag filament wire suitablefor use in incandescent lamps.

It is still another object to provide permissible and preferred processsteps and conditions for forming shockresistant, vibration-resistant andnon-sag filament wire suitable for use in incandescent lamps.

The aforesaid objects of the invention, and other objects which willbecome apparent as the description proceeds, are achieved by providing afilament and filament wire wherein the filament and wire have includedtherein a plurality of minute segregations which comprise thorium oxide,substantially all of which segregations are aligned in a plurality ofdiscontinuous groupings which are longitudinally disposed throughout thewire, that is, disposed in the direction of working. When the filamentis energized and recrystallizes, the crystals are elongated andinterlocking and follow the disposition of the segregation groupingswithin the wire. These interlocking crystals are maintained as such bythe aligned segregation groupings. There are also provided process stepsfor fabricating the wire, which process steps include a current-timesintering schedule which is necessary to the production of the instantfilament wire. There are also provided permissible and preferred rangesfor the doping material as well as permissible and preferred variationsin the process for forming the wire.

For a better understanding of the invention, reference should be had tothe accompanying drawings wherein:

FIG. 1 is .a fiow diagram illustrating the process steps involved inpreparing the improved wire;

FIG. 2 is a graph of sintering current expressed as a percent of ingotfusion current vs. time, which curve sets forth the percent of fusioncurrent-time relationship which is necessary to produce the instantwire;

FIG. 3 is a photomicrograph showing an etched section of the prior-.artpotassium, alumina and silica-doped wire, after recrystallization;

FIG. 4 is la photomicrograph of an etched section of the instant wirebefore recrystallization;

FIG. 5 is a photomicrograph of an etched section of the instant wire,after recrystallization, illustrating the interlocking crystalstructure;

FIG. `6 is a photomicrograph of an etched section of the instant wire asshown in FIG. 5, but taken at a higher magnification;

FIG. 7 is a photomicrograph of the same section of the instant wire asshown in FIG. 6, but taken at a stillhigher magnification;

FIG. 8 is a photomicrograph of an etched section of thoria-doped wire,.after recrystallization, wherein the permissible ingot .sinteringcurrent-time relationships as set forth in FIG. 2 have been exceeded;

FIG. 9 is a photomicrograph of an etched section of thoriadoped wire .asshown in FIG. 8, but taken at a higher magnification;

FIG. is a photornicrograph of the same section of thoria-doped wire asshown in FIG. 9, but taken at a stillhigher magnication.

In accordance with the general process steps as illustr-ated in FIG. 1,tun-gsten ore is digested and reacted to form ammonium paratungstate.This procedure is well known and includes as a nal step reactingammonium tungstate and hydrochloric acid to produce ammoniumparatungstate. To the ammonium paratungstate is added thorium nitrate inthe form of a water solution in concentration of 0.83 gram C.P. gradethorium nitrate in ten cc. of water, for example. The thorium nitrateand ammonium paratungstate are thoroughly admixed, as by stirring, toform a homogeneous paste. Thereafter the paste isk dried and is tired inair at a temperature at about 1000 C. for about two hours, for example,or until the ammonium paratungstate is converted to tungstic oxide (W03)and the thorium nitrate is converted to ThOZ. The firing temperature of1000 C. is given only by Way of example and may be varied considerably.The amount of thorium nitrate in the Vinitial admixture should be suchthat the percent by weight of thorium, expressed as the loxide, withrespect -to the tungsten, expressed as metal, is from to 4% andpreferably from to 11.%. As a specific example, the percent by weight ofthorium, expressed as the oxide, is 1% of the weight of the tungstenmetal in the admixture.

The admixed thorium oxide and tungstic oxide are then red in a reducingatmosphere such as dry hydrogen. As a specific example, a boatcontaining 100 grams of the admixture is fired in the dry-hydrogenatmosphere (maintaining a flow of fty cubic feet per hour), first at atemperature of about 640 C. for sixty minutes, lthen at a temperature ofabout 840 C. for sixty minutes and finally at a temperature of about1000o C. for another sixty minutes. This reducing schedule is dependenton the batch size and may be varied considerably. However, the foregoingschedule is very satisfactory. This will reduce the tungstic oxide tofinely-divided metallic tungsten and the thorium oxide will remain assuch. The finely-divided admixture of thorium oxide and tungsten metalpowder are then formed into pressed green in'gots. As a specificexample, 2050 grams of the admixture are pressed into an ingot havingdimensions of 0.725 inch by 0.655 inch by 24 inches and the pressureused to form the ingot is 17 tons per square inch. While the resultingpressed green ingot has suiicient strength to facilitate its bein-ghandled, where an electrical sintering technique is utilized it ishighly desirable to pre-sinter the ingot in order to render it moreself-sustaining in nature so that it may readily be clamped betweenelectrodes during electrical sintering. As a specific example, thepressed green ingot is pre-sintered in a dry-hydrogen atmosphere at atemperature of about 1000 C. for about 20 minutes, for example, using anelectrical furnace. This will impart to the green ingot .a sufficientamount of pre-sintering in order to render the ingot quiteself-sustaining. This pre-sintering schedule may be varied considerably.

The self-sustaining green ingot is then pla-ced in a vertical positionin an electrical sintering bottle, wherein the top end portion of -theingot is clamped between heavy molybdenum electrodes and a tungstencontact clamp connects to the bottom portion of the ingot and issuspended in a mercury pool to facilitate electrical contact. Electricalsintering is normally effected in a dry-hydro-gen atmosphere in adouble-walled copper bottle which prefer ably is water cooled, suchsintering bottles being well known. With an ingot of the aforementioneddimensions, a ow of hydrogen through the sintering bottle of 100 cubicfeet per hour has been found to be satisfactory.

The formation of the instant shock-resistant, vibrationresistant andnon-sag tungsten wire has been found to be dependent upon atemperature-time relationship, as will be explained in detailhereinafter. In addition, for the speciic ingot swaging schedules asgiven hereinafter,

it has been found necessary to sinter the ingot at a suiiicient currentand for a sufiicient time in order to impart to the ingot a sufficientdensity to enable it to be mechanically reduced in size (i.e., swagedand later drawn) without fracturing. For the specic ingot dimensions andswaging schedules considered herein, a sintered ingot density of atleast about 16.4 is desired and preferably the density of the sinteredingot is at least about 17.1. Normally the higher the ingot sinteringcurrent and the longer such sintering current is held, the greater thedensity of the resulting ingot. Ingot densities greater than thoseusually obtained (e.g., 17.1-17.8) normally are not afactor with regardto enabling a sintered ingot to be reduced in size without fracturing.By altering the swag` ing schedules to increase the temperatures atwhich the sintered ingot is swaged, the lower limit for the permissibleingot density may be extended, and vice-versa, if the swagingtemperatures for the ingot are decreased, the ingot desirably issintered so as to have at least the preferred minimum density. As aspecific example, a maximum ingot sintering current of about 72% of theingot fusion current, when maintained for about ve minutes, normallywill not produce an ingot of suficient density to enable it to be swagedwithout fracturing, unless special swaging precautions are taken. If theingot sintering time at this maximum ingot sintering current is extendedto about sixty minutes, the ingot normally can be swaged, according tothe schedule described hereinafter, without fracturing. Thus it can beseen that the selection of the minimum temperature-time relationshipsnecessary to enable the ingot to be mechanically reduced in size withoutfracture are a matter of choice and design and are dependent on ingotdimensions and swaging schedules as well as ingot sintering schedules.This requirement has existed with tungsten wire as manufactured inaccordance with the teachings of the prior art as well as the instantwire.

In the curve A-B in FIG. 2 are plotted R.M.S. currenttime relationshipsfor the sintering schedule for producing the instant wire, wherein themaximum ingot sintering current (expressed as a percent of ingot fusioncurrent) is plotted vs. time such current is maintained. Fusion ormelting current for the specific ingot described herein is 6700 amperes(60 c.p.s.). If the maximum sintering current is maintained for asuiiicient time to cause the plot of ingot sintering current vs. time tofall on or above the curve A-B in FIG. 2, the resulting sintered ingotcannot be formed into a filament which combines all the properties ofshock-resistance, vibrationresistance and non-sag characteristics. Ifthe plot of ingot sintering current vs. time falls below the curve A-Bin FIG. 2, the resulting ingot can be formed into shock-resistant,vibration-resistant and non-sag wire suitable for use in incandescentlamps, provided of course that the ingot has suiiicient density toenable it to be reduced in size without fracturing. Preferably the plotof ingot sintering current vs. time falls below curve C-D in FIG. 2 inorder to produce the best-possible filament. Manufacturing practiceswhere large production is involved must provide large tolerances inorder to keep costs as low as possible. The curve C-D in FIG. 2 takesinto account factory tolerances and in the usual factory practices, thecurve C-D will be used as a guide in the sintering schedule forproducing the instant wire. In addition, the formation of the instantwire involves a temperature-time relationship during sintering, as exlplained hereinafter, and it is desired to keep this temperature-timerelationship as low as possible commensurate with providing a sufficientdensity for the sintered ingot t-o enable it to be reduced in sizewithout fracturing.

The curves A-B and C-D are expressible by formulas as follows: sinteringcurrent where sintering current is expressed as a percent of the ingotfusion current and t in minutes is at least 2; sintering current wheresintering current is expressed as a percent of the ingot fusion currentand t in minutes is at least 5. Thus to produce the instant wire, thegreen ingot is electrically sintered at such sintering current and forsuch time that the resulting sintered ingot may be reduced in sizewithout fracturing and so that the plot of ingot sintering currentexpressed as a percent of ingot fusion current vs. time in minutes fallsbelow the curves represented by the foregoing formulas, with the choiceof curves which are represented by these formulas dependent on whetherthe permissible or preferred sintering schedule is to be followed;V

As a specific example for sintering an ingot as specified hereinbefore,in accordance with the instant process, following is a suitablesintering schedule:

Sintering current, R.M.S. Time current is amperes (60 c.p.s.): heldminutes 4800 1/2 5200 1/2 5400=80.7% of fusion amps l0 The maximumsintering current is normally held for a somewhat extended period and itis this maximum sintering current which is effective in causing theresulting wire to have the desired characteristics. In theabove-detailed sintering schedule, the sintering currents are increasedgradually. This is primarily because some impurities are present in thetungsten and it is desirable to volatilize all impurities as well as toconvert any remaining tungstic oxide to metallic tungsten beforeincreasing the sintering current to its maximum. If special precautionswere taken to purify to a high degree the constituents of the pressedand unsintered ingot, the initial sintering steps, wherein the ingotsintering current is gradually increased, could be shortenedconsiderably and the ingot sintering current raised to a maximum in amore rapid fashion. It is more economical, however, to eliminateimpurities by a sintering schedule such as the foregoing.

The curves A-B and C-D in FIG. 2 thus define the limits for thepermissible and the preferred ingot sintering currents and the timewhich such sintering currents may be maintained. As a specific exampleof an unsuitable sintering schedule for producing the instant wire, amaximum ingot sintering current of 87%-90% of ingot fusion current, whenmaintained for a period of twentyfive minutes, will describe a pointwhich falls above the curve A-B in FIG. 2. A maximum sintering currentof 80% of the ingot fusion current, when maintained for a period oftwenty minutes constitutes a permissible sintering schedule, although itis preferable to hold this maximum ingot sintering current of 80% of theingot fusion current for a period of about 10 minutes, for example.

After the ingot has been sintered for the prescribed time at theindicated currents, it is cooled within the sintering bottle whilemaintaining the stream of dry hydrogen thereover. Approximately 5% ofthe length dimension is removed from each end of the cooled and sinteredingot, since the sintering of these portions Will be uneven due to thecontact electrodes, such a procedure being standard sintering practice.The resulting sintered ingot is then heated to approximately 1600C.-1650 C. in a non-oxidizing atmosphere such as hydrogen and swagedthrough three swaging dies, using conventional swaging equipment andconventional swaging practices. This will produce a partially-swagedingot of generally-circular cross-sectional area, having a diameter ofapproximately 0.467 inch. The partially-swaged ingot is then annealed torelieve strains and annealing may be accomplished by passing a currentof 2600 amps. therethrough for a period of two minutes, whilemaintaining the partially-swaged ingot in a dry-hydrogen atmosphere.Thereafter the ingot is reheated to approximately 1350-1400 C. and isswaged through two swaging dies to a diameter of about 0.337 inch. Thepartially-swaged ingot is then reheated to about 1900 C. in anon-oxidizing atmosphere such as hydrogen `for about three minutes, inorder to relieve strains, and it is thereafter heated to about 1300 C.and swaged to a cross-sectional diameter 0.186 inch. Thepartially-swaged ingot is then annealed to a temperature of 1950 C. in anon-oxidizing atmosphere such as hydrogen for about one and one-halfminutes, reheated to about 1300 C. and reswaged to a cross-sectionaldiameter of about 0.083 inch.

The foregoing swaging procedures result in a greatlyelongated bar andafter the diameter of 0.083 inch is achieved, further reduction indiameter is achieved through hot-drawing, using conventional drawingequipment and conventional drawing practices. In the hotdrawingprocedure, the elongated material is heated to approximately 800 to 900C. and is reduced approximately 12% in diameter on each pass through adie. After approximately every fifth pass through the drawing dies, thedrawn material is annealed to relieve strains and an annealingtemperature of about 1700 C. in a nonoxidizing atmosphere such ashydrogen for about ten seconds is suitable. The drawing procedures arecontinued until the desired wire diameter is achieved, which as aspecific example is 1.23 mils. It should be understood that theforegoing swaging-annealing-swaging-drawingannealing-drawing proceduresare only given in detail by way of specific example and may -be variedconsiderably to produce substantially the same end effect. Also, whilethe foregoing swaging and later drawing schedules for the instant wirehave all been of a mechanical nature, it should be understood that thefinal reductions in wire size could be effected by other than mechanicalmeans, such as the electrolytic reduction process described in PatentNo. 2,784,154 to Korbelak et al.

After the wire has been drawn to size, it is formed into filament coilsby well-known techniques, and then incorporated into lamps. Suchfilament coils normally have a generally-helical configuration and insome cases the helical coils are again coiled to form a coiled-coil,such practices being usual in the art.

In FIG. 3 is shown a photomicrograph of a recrystallized and etchedsection of the best-available wire for applications requiringshock-resistant, vibration-resistant, and non-sag characteristics, whichwire is potassium, alumina and silica-doped, as noted hereinbefore. Whenlamp filaments Of such wire are initially energized, the tungstencomprising the filament recrystallizes and the doping additives causethe tungsten crystals to have either a single crystal or an interlockingstructure, or both. These crystal structures are subject to failureunder shock and vibration, although they display excellent non-sagcharacteristics.

In FIG. 4 is shown a photomicrograph (1000)() of an etched section ofthe instant wire before recrystallization. The photomicrograph of theetched wire discloses a plurality of minute segregations which aredistributed Within the wire and substantially all of these segregationsare aligned in a plurality of discontinuous groupings which arelongitudinally disposed throughout the wire. The

elongated crystal or grain boundaries appear as a series of continuouslines disposed in the direction of working. On recrystallization thesegrains will grow as shown in FIG. 5.

In FIG. is shown a photomicrograph (250)() of an etched section offilament wire manufactured in accordance with the instant proc'ess andenergized at its normal operating temperature for a sufficient time tocause recrystallization. This photomicrograph was taken at too low amagnification to show the general distribul tion of the minutesegregations which are included lwithin the wire. It does illustrate,however, the interlocking crystal struct-ure which is obtained after theinstant wire has been recrystallized and this photomicrograph is to becontrasted with the photomicrograph of FIG. 8.

The term interlocking crystal structure is generally used in thetungsten filament art to describe crystals or grains comprising thefilament which are elongated in the direction of working, with the endportions of the grains overlapping. This inhibits slippage at the grainboundaries since the overlapping structure locks the grains with respectto one another. It is this generallyaccepted meaning of the terminterlocking crystal structure which is used herein to describe thecrystal structure of th'e instant wire after recrystallization. The termrecrystallization as ygenerally used in the art, and as used herein,refers to the appearance of discrete, nearlyperfect crystalline grainswhich are formed upon initial energization of the filament at its normaloperating temperature. 'Such recrystallization may b'e demonstrated witha photomicrograph technique, as in the instant case. In FIG. 6 is shown-a photomicrograph (1000x) of an etched filament section manufactured inaccordance with the instant process and energized at normal operatingtemperature for a suicient time to cause recrystallization. Distributedwithin the lwire are a plurality of minute segregations, andsubstantially all of these segregations are aligned into segregationgroupings. These aligned segregations, which comprise thorium oxide andare of varying size, are aligned in single le and are quite similar towhat may be termed stringers. The ASM metals handbook, 1948 edition,defines stringers as A microstructural configuration of alloyconstituents or foreign material lined up in the direction of working.This definition closely fits the aligned segregation lgroupings as shownin FIGS. 4, 5, 6 and 7 except that the term Stringer normally infers acontinuous and elongated inclusion aligned in the direction of working.For this reason, it is -considered more correct to define the alignedand dot-like segregations as a plurality of discontinuous Stringer-likesegregation groupings which are formed by substantially all the minutesegregations included in the wire. The minute segregations are normallycircular in configuration, although some may be slightly elongated inthe direction of working. As seen in the photomicrographs of FIGS. 5 and6, the highly-magnified tungsten crystals are of an interlocking natureyand are elongated, with the elongated crystal dimensions generallyfollowing the disposition of the discontinuous Stringer-like segregationgroupings. Since the primary difference between the interlocking crystalstructure of the instant filament and the interlocking crystalstructures of the prior art are the discontinuous Stringer-likesegregation groupings, it is apparent that these segregation groupingsmaintain the crystals in their interlocking relationship to provideexcellent shock-resistant, Vibration-resistant and non-sagcharacteristics for the filament.

In FIG. 7 is shown an etched section of the same portion of the wire asshown in FIG. 6, except that the magnification is 2000 and this betterillustrates the disposition of the minute segregations within the wire.As seen in this high-magnication photomicrograph, only a few of thesegregations are randomly distributed within the wire, that is, notaligned into the segregation groupings and substantially all of theminute segregations included within the wire are aligned into thediscontinuous Stringer-like segregation groupings.

In FIG. 8 is shown a photomicrograph (250)() of an etched section ofthoria-doped wire, after recrystallization, which wire is representativeof an ingot sintered at 87% of its fusion current for a period oftwenty-five minutes. This photomicrograph was taken at too low amagnification to show the general distribution of the minutesegregations which are included within the wire. It does illustrate,however, the random crystal structure, which approaches what is known inth'e art as an equiaX structure, which is obtained after the wire isrecrystallized. This photomicrograph is to be contrasted with thephotomicrograph of FIG. 5.

In FIG. 9 is shown a photomicrograph 1000 of an etched section ofthoria-doped wire, similar to that shown in FIG. S, but with a lgreatermagnification. As shown, the minute segregations are distributedthroughout the wire in a relatively-random fashion. While some of thesegrations have remained in the aligned groupings, a considerableportion have migrated into -a generally-random distribution throughoutthe wire.

The generally-random distribution of a considerable portion of thesegregations included in such wire is better illustrated in thephotomicrograph shown in FIG. l0, which is of the same section of thewire as shown in FIG. 9, but with a still-higher magnification (2000 Asclearly shown in this photomicrograph, a considerable portion of theminute segregations are scattered in random fashion throughout the wire.

It is very difficult to determine actual particle sizes of the minutesegregations within the wire when using an etching and photomicrographtechnique, -since some of the tungsten around the etched particles isalso dissolved. This gives a false impression of the actual size of thesegregations. However, it is clear from an observation of thephotomicrographs shown in FIGS. 6, 7, 9 and 10 that where thethoria-doped ingot is sintered at such current and for such time so asto cause the plot of sintering current Vs. time to -fall on or above thecurve A-B in FIG. 2, some of the segregations included within theresulting wire are somewhat coagulated, as compared to the segregationsincluded within wire processed according to the instant teachings. Thisis in addition to being considerably random in distribution within thewire. Such filament wire as shown in FIGS. 8, 9 and l0, whenincorporated into an incandescent lamp, will sag very rapidly,apparently because of slippage at the crystal boundaries. Thephotomicrographs shown in FIGS. 4 through 10 were taken of wire whichhad been drawn to a diameter of 0.043 inch. The appearance of the wireat this diameter is representative of the appearance of such wire drawnto a smaller diameter, except that the longitudinal distance between theindividual segregations increases as the wire is drawn to a smallersize.

As noted hereinbefore, the percent by weight of thorium oxide mayvaryfrom 14% to 4% by weight of the tungsten. At less than 1i% by weightthorium oxide, the beneficial effects which are realized through theStringer-like segregation groupings are minimized and at more than 4% byweight thorium oxide, difficulties are encountered in swaging the ingot.It is preferred to use from to l1/2% by weight of the tungsten ofthorium oxide as a doping additive. Within this preferred range, fewdifiiculties are encountered in swaging the ingot and there issufiicient doping additive present to provide maximum benefit withrespect to shockresistant, vibration-resistant and non-sagcharacteristics for the filment wire.

In the foregoing specific example, the sintering and annealingatmosphere is dry hydrogen. The dry hydrogen as used has a dewpoint ofabout minus 60 F. It should be understood that hydrogen containingappreciably more moisture can be tolerated. Also, hydrogen containingsubstantially no moisture can be used and the foregoing moisture contentof the hydrogen has been given only by way of example. It is 4alsopossible to use other non-oxidizing atmospheres in sintering andannealing, such as rare gas atmospheres, or even vacuum, but it iseconomically desirable to use hydrogen.

Vibration and shock resistance for incandescent filaments is bestmeasured on a performance basis. In one test which simulates the shocksto which toy train lamps lare subjected, the lamps are mounted on ametallic plate. The plate is then struck a series of impacts undercarefully-controlled conditions. Lamps which incorporated the instant-laments were mounted in this shock tester and were subjected to 1000shocks. At the end of this test, 76% of the lamps incorporating theinstant improved filament would still operate.V Similar lamps which wereprovided with the prior-art potassium, alumina and silicadoped wire weremounted in the shock tester and after 1000 impacts, only 8% of theseprior-art lamps would still operate. While the test was extremelysevere, it nevertheless simulates the shocks to which such lamps aresubjected when they are used and the performance test illustrates thealmost phenomenal strength which the instant non-sag wire possesses.Other applications which require a very high-strength wire areautomobile radio and panel lighting and automobile trunk lights wherethe lamps are subjected to the shocks of automobile vibrations and thetrunk being slammed shut. In all tests simulating the shocks andvibrations which lamps receive in such applications, the instant wiredisplays an outstanding superiority over the best-available shockandvibration-resistant, non-sag wire of the prior art. It should be notedthat the instant wire operates with slightly less efficiency than thebest prior-art doped wire. It is not possible, however, even to approachthe performance of the instant improved wire by operating the bestprior-art doped wire at a lower temperature, which simulates loweroperational efficiency.

As noted hereinbefore, thoria doping of tungsten has been reported manytimes, with the patent and other art extending back to the early 1900s.The best of these thoria-doping techniques, however, produced wire whichwas subject to considerable sag and the general performance of suchthoria-doped wire is summarized in Patent No. 2,114,426 to Laise. It wasprimarily for these reasons that the thoria-doped wire was replaced bythe presently-used potassium, alumina and silica-doped wire.Thoria-doped tungsten has also been used in fabricating weldingelectrodes where the electron-emissivity of the thoria facilitatesstriking and maintaining the welding arc. In the prior-art processingfor thoria-doped tungsten, the best-accepted procedure has been tosinter the ingots at a maximum current of about 87% to 92% of the ingotfusion current and to maintain this maximum sintering current for abouttwenty-five minutes. As shown in FIG. 2, this will not produce amaterial which can be swaged and drawn to form shock-resistant,vibration-resistant and non-sag filament wire for incandescent lamps. Inthe foregoing shock and vibration tests, the best thoria-dope-d tungstenfilaments of the prior art would be generally suitable from thestandpoint of shock and vibration resistance. Lamps incorporating suchfilaments, however, would fail quickly from filament sag since the usualfilament design will not tolerate any appreciable sag.

The processing of the instant wire involves a temperature-timephenomenon, wherein the temperature parameter, during sintering, hasbeen represented as ingot sintering current, expressed as a percentageof ingot fusion current. At excessively high sintering temperatureswhich are maintained for an appreciable sintering period, swaging anddrawing such a sintered ingot will not produce the Stringer-likegroupings in the resulting filament Wire, which Stringer-like groupingsare required to direct the crystal growth into an interlocking structureand maintain same during lamp operation. Thus to produce the instantwire, the sintering current-time relationships must be kept relativelylow, as compared to the practices of the prior art. It should be notedthat X-ray diffraction studies of the instant wire disclose only thepresence of thoria and tungsten. The presence of some limited amounts ofthoium-tungsten complexes should not be excluded, however, even thoughthese are not indicated in the X-ray diffraction studies. In addition,some impurities in the doping material may be tolerated and these havenot been observed to affect deleteriously the quality of the wire.

It has been found that the instant wire will best perform in theexceptional manner indicated hereinbefore when the lamps in which it isused are of a type which operate with a relatively low efficiency, suchas miniature types as used in panel lighting, toy trains, etc. Thefilament operating temperatures for such lamps are in the order of about2050 C. to about 2430 C., as contrasted with a standard gas-filled10U-watt lamp which operates at a filament temperature of about 2600 C.In the operation of lamps incorporating the instant improved wire, thetemperature-time relationship which governs the formation of thediscontinuous, Stringer-like segregation groupings is also present andthe higher the operating temperature of the lamps, the faster thesegregations depart from the Stringer-like formations to a randomdisposition. When an appreciable portion of the Stringer-like formationsof segregation groupings have migrated to form random segregations, thecrystals within the wire grow further, the interlocking structuresdisappear, and at this point the filament sags and fails throughshorting out turns of the filament coil.

The foregoing observations are substantiated by further control studies.As the miniature-type, low-efiiciency lamps which incorporate theinstant wire are operated, their performance is excellent underconditions of vibration and shock. Between 1000 and 1500 hours, anappreciable portion of the Stringer-like groupings disappear and formrandomly distributed particles and when this occurs, the Wire sags andthe lamp fails. This temperature-time dependence for the migration ofthe segregations from the Stringer-like groupings is additionallysubstantiated by incorporating the instant wire into so-calledhigh-efficiency lamps where the filament is operated at a much highertemperature. Here the performance of the instant wire, from thestandpoint of life, is not as good and the lamp filament sags and failsat an earlier time. At failure of both the low-efficiency andhigh-efliciency lamps, photomicrographs of the etched filaments whichfailed show a migration of a considerable portion of the Stringer-likesegregation groupings into random particles or segregations.

While the instant wire when used in so-called highefficiency lamps willresult in relatively short lamp life, it should `be understood thatshorter life for high efiiciency lamps is not objectionable in allcases, particularly where shock and vibration resistance are of primeimportance. For some applications, a shorter lamp life can be toleratedfor the sake of the other attributes of the instant wire. Again it ispointed out that the instant non-sag filament wire is almost phenomenalin its strength under vibration and shock and far surpasses any filamentwire heretofore reported.

In the foregoing specific example, thorium nitrate was added to theammonium paratungstate before the paratungstate was converted totungstic oxide. Thorium compounds which convert to the oxide on heatingcan be substituted for the thorium nitrate, specific examples beingthorium hydroxide or thorium oxalate, using dry-mix techniques wherenecessary. Also, thorium oxide can be added as such to the ammoniumparatungstate. In addition, any of the aforementioned thorium-containingcompounds, for example, can be added directly to the tungstic oxide oreven to the tungsten metal powder. In .a case c'an be admixed as dopingmaterial, such as an admixture of equal proportions of thorium nitrateand thorium hydroxide. It should be understood that in all cases theweight ratio -of thoriumr expressed as the oxide, to tungsten should bemaintained within the aforementioned thorium oxide to tungstenlimitations. It is thus apparent that the essential steps of the processinvolve forming an admixture of thorium oxide and tungsten metal powderwithin the aforementioned constituent weight percentages, forming thegreen ingot, sintering the green ingot at the effective sinteringcurrents in accordance with the schedules established by the curves A-Bor C-D in FIG. 2, and thereafter reducing the sintered ing-ot into wireof the desired size. It is preferred, however, to add the thoriumnitrate to the ammonium paratungstate, as given in the foregoing specicexample.

A consideration of the curves A-B and C-D in FIG. 2 will show that onlythe maximum sintering currents have an appreciable effect on thecurrent-time relationships which are present during sintering and whichaffect the later performance of the filament wire. It is possible to usea step-ladder sintering procedure at the effective sintering currents,wherein the effective sintering currents may be varied and held forrelatively short periods of time. If a step-ladder type of sinteringschedule at the higher effective ingot sintering currents is to be used,the summation of percentages `of ingot sintering times for the ingotsintering currents used should be less than 100%, where the 100%abscissa value corresponding to any ingot sintering current, expressedas :a percent of ingot fusion current, `is established by thecorresponding abscissa values of the curves A-B or C-D in FIG. 2,depending on whether a permissible or preferred sintering schedule isdesired. As an example, if an ingot is sintered at 71% of `fusionamperes for a period of twenty minutes, it will have been sintered forapproximately 11% of the maximum permissible sintering time at thiscurrent. Thereafter, if the `ingot sintering current is increased to 75%`of fusion amperes and the ingot is sintered for twenty minutes at thissintering current, lit will have been sintered for approximately 25% ofthe maximum permissible sintering time at this sintering current.Thereafter, if the ingot sintering current is increased to 78% of fusionamperes and it is sintered at this current for approximately tenminutes, it will have been sintered for approximately 22% of the maximumpermissible sintering time at this sintering current. Finally the ingotmay :be sintered at a current of 80% of fusion amperes for six minutes,which represents approximately 18% of the maximum permissible sinteringtime at this sintering current. Adding the foregoing percentages, theingot will have been sintered for a total of 76% of its maximumpermissible sintering, if wire in accordance with the instant teachingsis to result. As an example of a step-ladder sintering process for thepreferred sintering schedule, 70% of fusion amperes for twenty minutes,then 75 of fusion amperes for ten minutes, then 78% of fusion amperesfor six minutes and nally 80% of fusion amperes for ve minutes willresult in the ingot having been sintered for approximately 81% of itsmaximum preferred sinterang.

The fusion current for the doped ingot will vary somewhat with thedoping constituents. As an example, where the ingot is doped with theprior-art potassium, alumina and silica-doping constituents, the ingotfusion temperature is somewhat lower than for a correspondingthoriadoped ingrot. This is probably because these prior-art dopingconstituents normally result in increasing the electrical resistance ofthe ingot. With a higher electrical resistance, less sintering currentis required to produce the same temperature, so that the currentrequired for fusion of the ingot is slightly lower. In thoriadoped wire,the concentration of residual doping material after sintering isapproximately the same as the concentration of the doping materialbefore sintering. This is contrary to the usual prior-art wire, which asan example may contain residual doping material, after sintering, inconcentrations of 1000 parts per million alumina, 1000 parts per millionsilica and to 400 parts per million potassium. Experiments have beenconducted wherein equal proportions of thoria-doped tungsten metalpowder and the prior-art potassium, alumina and silica-doped tungstenmetal powder were admixed and sintered in accordance with a schedulewhich would produce the instant non-sag vibrationand shock-resistantwire. Since most of the alumina, silica and potasium are volatilizedduring the sintering, the thoria-d'oping predominates and satisfactoryshookand vibration-resistant, non-sag wire is produced. The fusioncurrent for such an admixed green ingot is slightly lower, but thecurrent-time relationships as shown in the curves A-B or C-D in FIG. 2must still be followed. Thus the instant Wire may be produced where thegreen ingot contains only an appreciable proportion of the thoria, asdoping material, provided the percentages of the thoria with respect tothe total tungsten metal are maintained within the aforementionedranges. In addition, the presence of other refractory oxides added asdoping constituents may be tolerated in the instant wire. As an example,10% by weight of the thoria of ceria has not been found to effectdeleteriously the perfonnance of the instant wire.

FDhe preferred ingot sintering technique, as detailed hereinbefore, isan electrical sintering technique, wherein a high current is passedthrough the green ingot to effect the sintering. This may be defined aselectrical-resistance sintering. Ingot sintering may `also ybeaccomplished by an induction-heating technique using an ingot asspecified hereinbefore, for example, and effecting the sintering in anon-oxidizing atmosphere, preferably hydrogen, in a manner as detailedheretofore. Where induction-'heating sintering olf the ingot is used,the effective ingot sintering temperatures should be the same `as whereelectricalresistance ingot sintering is used, ysince the formation ofthe instant wire is dependent upon a temperature-time sinteringschedule, as explained in detail. In order to correlateinduction-heating sintering schedules with electricalresistancesintering schedules, the electrical-resistance sintering bottle may beprovided with a protected sighting window through which opticalpyrometer temperature readings of the ingot may be correlated with ingotsintering current, expressed as a percent of ingot fusion current.Induction-heating apparatus suitable for sintering a green ingot iscommercially available. In correlating the induction-heating schedules,a protected sighting window may 'also be provided through theinduction-heating furnace. With the same-size ingot and the sainedry-hydrogen atmosphere during sintering, the same effective ingotsintering temperatures must be maintained for the same times as where anelectrical-resistance sintering technique is used, if the instant wireis to be produced. Accordingly, proper induction-heating sinteringschedules may be correlated by the optical pyrolmeter ingot sinteringtemperatures previously taken. Thus when using an inductionheatingtechnique for sintering the green ingot to produce Ithe instant wire,the ingot should be sintered -at such ternperature and for such timethat the sintered ingot can be mechanically reduced in size wihoutfracturing. In addition, the effective ingot sintering temperaturesshould be those which are obtained with an electrical-resistancesintering technique. These effective sintering temperatures may beexpressed -as equivalent ingot sintering currents in terms of percent ofingot fusion current which, when plotted vs. time in minutes that thesintering temperature (expressed as current) is maintained, must fallbelow the curve A-B or C-D in FIG. 2, depending on whether a permissibleor preferred sintering schedule is to be used.

It should be understood that while specific sintering schedules havebeen outlined for an ingot of specific dimensiolns, varying the ingotdimensions will alter the fusion current for the ingot and thus alterthe specific sintering currents as given hereinbefore. However, theingot sintering currents, when expressed as a percent of ingot fusioncurrent, are for practical purposes independent of the ingot dimensions.Thus the permissible and preferred ingot sintering schedules establishedby the curves A-B and C-D in FIG. 2 are for practical purposesindependent olf ingot dimensions.

In the foregoing description, specific ingot dimensions andcharacteristics as well as specific sintering schedules Were -outlinedin detail. It should be clear that the specitic ingot dimensions,sintering techniques and schedules can be modified, provided the ingotsintering temperature (as expressed by current) vs. time relationshipsas established `by the curves A-'B and C-D in FIG. 2 are followed. Thusno matter what the ingot sintering technique or schedule, the greeningot should be sintered at such temperature yand for such time that theresulting sintered ingot can be mechanically reduced in size withoutfracturing. In addition, the ingot sintering temperatures `and ingotsintering times should be equal to those ingot sintering temperaturesand ingot sintering times which are obtained when electrical-resistancesintering an ingot as detailed hereinbefore, with the plot of ingotsintering current expressed `as a percent of ingot fusion currentfalling below the curve A-B or C-D, depending on whether a permissibleor preferred sintering schedule is to be followed. Ingot sinteringtemperatures may be correlated with an optical pyrometer technique, asdescribed hereinbefore. Thereafter the sintered ingot may be formed intowire by swaging and drawing as described in detail hereinbefore.

It will be recognized that the objects of the invention have beenachieved by providing shock-resistant, vibration-resistant and non-sagfilament wire and filaments suitable for use in incandescent lamps,which filaments comprise a plurality of interlocking crystals which aremaintained as such during operation of the lamp. .In addition, therehave been provided a process for forming such filament wire, includingpermissible and preferred process steps and conditions for lforming suchwire.

While in accordance with the patent statutes, one best embodiment of theinvention has been illustrated and described in detail, it is to beparticularly understood that the invention is not limited thereto orthereby.

I claim:

1. A shock-resistant, vibration-resistant and non-sag filament wiresuitable for use in incandescent lamps, said wire colmprising from 96%to 99% by weight tungsten and from 4% to 1A by weight thorium oxide, aplurality of minute segregations comprising said thorium oxidedistributed within said wire, and a plurality of discontinuousStringer-like segregation groups formed by substantially all of saidminute segregations and distributed throughout said wire.

2. A shock-resistant, vibration-resistant and non-sag lament wiresuitable for use in incandescent lamps, said wire comprising from 981/2%to 99%% by weight tungsten and from 11/2% to by weight thorium oxide, `aplurality of minute segregations comprising said thorium oxidedistributed within said wire, and a plurality `of discontinuousStringer-like segregation groupings formed by substantially all of saidminute segregations and distributed throughout said wire.

3. A shock-resistant, vibration-resistant `and non-sag filament forincandescent lamps, comprising a wire coiled in a generally-helicalconfiguration, said wire comprising from 96% to 99%% by weight tungstenand from 4% to by weight thorium oxide, a plurality of minutesegregations comprising said thorium oxide distributed within said wire,and substantially all of said segregations aligned in a plurality ofdiscontinuous Stringer-like groupings disposed throughout said Wire.

4. A shock-resistant, vibration-resistant and non-sag filament forincandescent lamps, comprising a wire coiled in a generally-helicalconfiguration, said wire comprising from 981/2% to 99%% by weighttungten and from 11/2% to by lWeight thorium oxide, a plurality ofminute segregations comprising said thorium oxide distributed withinsaid wire, and substantially all Iof said segregations aligned in aplurality of discontinuous Stringer-like groupings disposed throughoutsaid wire.

5. A shock-resistant, vibration-resistant and non-sag recrystallizedfilament for incandescent lamps, said filament comprising a wire coiledin a generally-helical configuration, said wire comprising a pluralityof interlocking crystals and containing from 96% to 99%% by weighttungsten and from 4% to 1A by weight thorium oxide, a plurality ofminute segregations comprising said thorium oxide distributed withinsaid wire, a plurality of discontinuous Stringer-like segregationgroupings formed by substantially all of said minute segregations, andthe interlocking crystals of said wire being elongated with theelongated crystal dimensions generally following the disposition of saidsegregation groupings.

6. A shock-resistant, vibration-resistant and non-sag recrystallizedfilament for incandescent lamps, said filament comprising a wire coiledin a generally-helical configuration, said wire comprising a pluralityof interlocking crystals and containing from 981/2% to 9911% by weighttungsten and from 11/2% to by weight thorium oxide, a plurality ofminute segregations comprising said thorium oxide distributed withinsaid wire, a plurality of discontinuous Stringer-like segregationgroupings formed by substantially all of said minute segregations, andthe interlocking crystals of said Wire being elongated with theelongated crystal dimensions generally following the disposition of saidsegregation groupings.

7. The process of forming shock-resistant, vibrationresistant andnon-sag filament wire suitable for use in incandescent lamps, comprisingforming an admixture of tungsten metal powder and doping materialcomprising thorium oxide, the percent by weight of thorium oxide beingfrom 1A% to 4% by weight of the admixed tungsten, forming said admixtureinto a self-sustaining green ingot, electrically sintering said greeningot under nonoxidizing conditions at such sintering current and forsuch time that the resulting sintered ingot can be mechanically reducedin size without fracturing and so that the plot of ingot sinteringcurrent expressed as a percent of ingot :fusion current vs. time fallsbelow the curve A-B in FIG. 2, and thereafter reducing said sinteredingot into wire of the desired size.

8. The process of forming shock-resistant, vibrationresistant andnon-sag filament wire suitable for use in incandescent lamps, comprisingforming an admixture of tungsten metal powder and doping materialcomprising thorium oxide, the percent by weight of thorium oxide beingfrom to l1/2% by weight of the admixed tungsten, forming said admixtureinto a self-sustaining green ingot, electrically sintering said greeningot under non-oxidizing conditions at such sintering current and forsuch time that the resulting sintered ingot can be mechanically reducedin size without fracturing and so that the plot of ingot sinteringcurrent expressed as a percent of ingot fusion current vs. time fallsbelow the curve C-D in FIG. 2, and thereafter reducing said sinteredingot into wire of the desired size.

9. The process of forming shock-resistant, vibrationresistant andnon-sag filament wire suitable for use in incandescent lamps, comprisingforming an admixture of tungsten metal powder and doping materialcomprising thorium oxide, the percent by weight of thorium oxide beingfrom 1t% to 4% by weight of the admixed tungsten, for-ming saidadmixture into a self-sustaining green ingot, electrically sinteringsaid green ingot in a hydrogen atmosphere at such sintering current andfor such time that the density of the sintered ingot is at least about16.4 and so that the plot of ingot sintering current expressed as apercent of ingot fusion current vs. time falls below the curve A-B inFIG. 2, and thereafter reducing said sintered ingot into wi-re of thedesired size.

10. The process of forming shock-resistant, vibrationresistant andnon-sag filament wire suitable for use in incandescent lamps, comprisingforming an admixture of tungsten metal powder and doping materialcomprising thorium oxide, the lpercent by weight of thorium oxide beingfro-m to 11/2% by weight of the admixed tungsten, forming said admixtureinto a self-sustaining green ingot, electrically sintering said greeningot in a dry-hydrogen atmosphere at such sintering current and forsuch time that the density of the sintered ingot is at least about 17.1and so that the plot of ingot sintering current expressed as a percentof ingot fusion current vs. time falls below the curve C-D in FIG. 2,and thereafter mechanically reducing said sintered ingot into wire ofthe desired size.

11. The process of `forming shock-resistant, vibrationresi-stant andnon-sag filament wire suitable for use in incandescent lamps: comprisingforming an admixture of tungsten metal powder and doping materialcomprising thorium oxide, the percent by weight of thorium oxide beingfrom 1A to 4% by weight of the admixed tungsten; forming said admixtureinto a self-sustaining green ingot; electrically sintering said greeningot under non-oxidizing conditions at such ingot sintering currentsand for such time that the resulting sintered ingot can be mechanicallyreduced in size without fracturing, and so that the summation ofpercentages of ingot sintering times for the effective ingot sinteringcurrents are less than 100%, where the 100% abscissa value correspondingto any ingot sintering current, expressed as a percent of ingot fusioncurrent, is established by the corresponding abscissa value of the curveA-B in FIG. 2; and thereafter mechanically reducing said sintered ingotinto filament wire of the desired size.

12. The process of forming shock-resistant, vibrationresistant andnon-sag filament wire suitable for use in incandescent lamps: comprisingforming an admixture of at least one of the group consisting offinely-divided tungsten metal powder and tungsten-containing compoundwhich is reducible to tungsten metal powder, and doping materialcomprising at least one of the group consisting of finely-dividedthorium oxide and finely-divided thoriumcontaining compound which isconvertible to thorium oxide; the percent by weight of admixedthorium-compound doping material expressed as thorium oxide being fromto 11/ 2% by weight of the tungsten expressed as metal; convertingthorium-containing compound into thorium oxide; reducing tungstencompound to tungsten metal powder; forming said admixed tungsten metalpowder and doping material into a self-sustaining green ingot;electrically sintering said green ingot under nonoxidizing conditions atsuch ingot sintering currents and for such time that the resultingsintered ingot can be mechanically reduced in size without fracturing,and so that the summation of percentages of ingot sintering times forthe effective ingot sintering .currents are less than 100%, where the100% abscissa value corresponding to any ingot sintering current,expressed as a percent of ingot fusion current, is estabilshed by thecorresponding 16 abscissa value of the curve C-D in FIG. 2; andthereafter mechanically reducing said sintered ingot into filament wireof the desired size.

13. The process of forming shock-resistant, vibrationresistant andnon-sag filament wire for use in incandescent lamps, comprising formingan admixture of finely-divided ammonium paratungstate and finely-dividedthorium nitrate, the percent by weight of thorium nitrate expressed asthorium oxide being from 1% to 11/2 by weight of the admixed tungstencompound expressed as tungsten metal, converting said ammoniumparatungstate to tungstic oxide and converting said thorium nitrate tothorium oxide, reducing said tungstic oxide to tungsten metal powder,forming said admixed tungsten metal powder and thorium oxide into aself-sustaining green ingot, electrically sintering said green ingot ina dry-hydrogen atmosphere at such sintering current and for such timethat the density of the sintered ingot is at least about 16.4 and sothat the plot of ingot sintering current expressed as a percent of ingotfusion current vs. time falls below the curve C-D in FIG. 2, andthereafter mech-anically reducing said sintered ingot into wire of thedesired slze.

14. The process of forming shock-resistant, vibrationresistant andnon-sag filament wire suitable for use in incandescent lamps, comprisingforming an admixture of tungsten met-al powder and doping materialcomprising thorium oxide, the percent by weight of thorium oxide beingfrom Mi to 4% by weight of the admixed tungsten, forming lsaid admixtureinto a self-sustaining green ingot, electrically sintering said greeningot under non-oxidizing conditions at such sintering current and forsuch time that the resulting sintered ingot can be mechanically reducedin size without fracturing and so that the plot of ingot sinteringcurrent expressed as a percent of ingot fusion current vs. time inminutes falls below the curve represented by the formula:

where t is expressed in minutes and is at least 2, and thereafterreducing said sintered ingot into wire of the desired size.

15. The process of forming shock-resistant, vibrationresistant andnon-sag filament wire suitable for use in incandescent lamps, comprisingforming an admixture of tungstenmetal powder and doping materialcomprising thorium oxide, the percent by weight of thorium oxide beingfrom to 11/2% by weight of the admixed tungsten, forming said admixtureinto a self-sustaining green ingot, electrically sintering said greeningot in a dry-hydrogen atmosphere at such sintering current and forsuch time that the resulting sintered ingot may be mechanically reducedin size without fracturing and so that the plot of ingot sinteringcurrent expressed as a percent of ingot fusion current vs. time inminutes falls below the curve represented by the formula:

sintering current :69.5-l-(8.3)(e-t/)i(10.4)(ert/18-5) where t isexpressed in minutes and is at least 5, and thereafter reducing saidsintered ingot into wire of the desired 16. The process of formingshock-resistant, vibrationresistant and non-sag filament wire suitablefor use in incandescent lamps: comprising forming an admixture oftungsten metal powder and doping material comprising thorium oxide, thepercent by weight of thorium oxide being from 1t% to 4% by weight of thetungsten; forming said admixture into a self-sustaining green ingot;sintering said green ingot under non-oxidizing conditions at suchtemperature and for such time that said sintered ingot can bemechanically reduced in size without fracturing, and so that the ingotsintering temperatures are those as obtained with anelectrical-resistance sintering technique with the plot of ingotsintering temperature, expressed as equivalent ingot sintering currentin terms of percent of ingot fusion current, Vs. time falling below thecurve A-B in FIG. 2; and thereafter reducing said sintered ingot intowire of the desired size.

17. The process of forming Ishock-resistant, vibrationiresistant andnon-sag lament wire suitable for use in incandescent lamps: comprisingforming -an admixture of tungsten metal powder and doping materialcomprising thorium oxide, the percent by weight of thorium oxide beingfrom to 11/2% by weight of the tungsten; forming said admixture into aself-sustaining green ingot; sintering said green ingot in adry-hydrogen atmosphere at such temperature and for such time that saidsintered ingot can be mechanically reduced in size without fracturing,and so that the ingot sintering temperatures are those as obtained withan electrical-resistance sintering technique with the plot of ingotsintering temperature,

expressed as equivalent ingot sintering current in terms of percent ofingot fusion current, Vs. time falling below the curve C-D in FIG. 2;-and thereafter reducing said sintered ingot into wire of the desiredsize.

18. The process of forming shock-resistant, Vibrationresistant andnon-sag lament wire suitable for use in incandescent lamps: comprisingforming an admixture of tungsten metal powder and doping materialcomprising thorium oxide, the percent by Weight of thorium oxide beingfrom 11% to 4% by weight of the tungsten; forming said admixture into yaself-sustaining green ingot; `sintering said green ingot at 4suchtemperatures and for such times that the resulting sintered ingot can bemechanically reduced in size without fracturing and so that the ingotsintering temperatures and ingot sintering times are equal to thoseingot sintering temperatures and ingot sintering times obtained whenelectrical-resistance sintering a green ingot so that the plot of ingotsintering current expressed -as `a percent of ingot -fusion current Vs.time falls below the curve A-B in FIG. 2, wherein theelectrical-resistance-sintered ingot has green ingot dimensions of 0.725inch by `0.655 inch by 24 inches and an ingot fusion current of 6700amperes; and thereafter reducing said sintered ingot into wire of thedesired size.

19. The process of forming shock-resistant, vibrationresistant andnon-sag lament wire suitable for use in incandescent lamps: comprisingforming an Aadmixture of tungsten metal powder and doping materialcomprising thorium oxide, the percent by weight of thorium oxide beingfrom to l1/2% by weight of the tungsten; forming said admixture into aself-sustaining green ingot; sintering said green ingot at suchtemperature and for such time that the resulting sintered ingot can bemechanically reduced in size without racturing and so that the ingotsintering temperatures and ingot sintering times are equal to thoseingot sintering temperatures and ingot sintering times obtained whenelectrical-resistance sintering a green ingot so that the plot of ingotsintering current expressed as a percent of ingot fusion current vs.time falls below the curve C-D in FIG. 2, wherein theelectrical-resistance-sintered ingot has green ingot dimensions of 0.725inch by 0.6155 inch by 24 inches and an ingot fusion current of 6700amperes; and thereafter reducing said sintered ingot into wire of thedesired size.

References Cited by the Examiner UNITED STATES PATENTS 1,082,933 12/1913Coolidge 75-176 1,461,140 7/1923 Ramage 75-'176 OTHER REFERENCES Li etal.: Tungsten, publ. by Reinhold Publ. Co., 3rd ed. (1955), pp. 21S-228.

L. DEWAYNE RUTLEDGE, Primary Examiner.

ROGER L. CAMPBELL, WILLIAM G. WILES,

Examiners.

O. R. VERTIZ, R. L. GRUDZIECKI,

A ssislant Examiners.

1. A SHOCK-RESISTANT, VIBRATION-RESISTANT AND NON-SAG FILAMENT WIRESUITABLE FOR USE IN INCANDESCENT LAMPS, SAID WIRE COMPRISING FROM 96% TO99 3/4% BY WEIGHT TUNGSTEN AND FROM 4% TO 1/4% BY WEIGHT THORIUM OXIDE,A PLURALITY OF MINUTE SEGREGATIONS COMPRISING SAID THORIUM OXIDEDISTRIBUTED WITHIN SAID WIRE, AND A PLURALITY OF DISCONTINUOUSSTRINGER-LIKE SEGREGATION GROUPS FORMED BY SUBSTANTIALLY ALL OF SAIDMINUTE SEGREGATIONS AND DISTRIBUTED THROUGHOUT SAID WIRE.
 7. THE PROCESSOF FORMING SHOCK-RESISTANT, VIBRATIONRESISTANT AND NON-SAG FILAMENT WIRESUITABLE FOR USE IN INCANDESCENT LAMPS, COMPRISING FORMING AN ADMIXTUREOOF TUNGSTEN METAL POWDER AND DOPING MATERIAL COMPRISING THORIUM OXIDETHE PERCENT BY WEIGHT OF THORIUM OXIDE BEING FROM 1/4% TO 4% BY WEIGHTOF THE ADMIXED TUNGSTEN, FORMING SAID ADMIXTURE INTO A SELF-SUSTAININGGREEN